1. Field of the Invention
The present invention relates to medium formation technologies and, more particularly, the present invention relates to a medium substrate, having a textured surface, which can be used as a substrate or support in magnetic recording mediums and the like, and a production method therefor. The present invention also relates to a magnetic recording medium using the medium substrate, a production method therefor, and a magnetic disk device having installed therein the magnetic recording medium.
2. Description of the Related Art
As is well known, various disk devices are used as external memory units of computers. A magnetic disk device records or reproduces the data with a magnetic head flying close to a disk. For this method of recording and reproducing data, a so-called CSS (contact start stop) system is generally employed, where the magnetic head contacts the disk surface when the disk is stationary, and the magnetic head slides on the disk while contacting therewith when the disk is actuated or stopped.
On the magnetic disk used in the CSS system, appropriately finely roughened surface asperities called xe2x80x9ctexturexe2x80x9d are formed so as to prevent stiction (a phenomenon of the head being adsorbed to the disk surface; this may cause failure of the disk to rotate or deformation or breaking of the head supporting system) or reduce the friction against the head.
The texture formation (namely, texturing) on the magnetic disk is performed using various methods. In general, a mechanical system using an abrasive tape or an abrasive slurry is employed. For example, in the case of forming a texture on the surface of an Nixe2x80x94P substrate, scratches are formed over the area in the circumferential direction on the substrate surface using a coarse abrasive tape and then the surface is lapped using a fine tape. In this method, however, the abrasive grains are fixed to the tape, burs are generated and this causes a problem. The lapping to remove these burs is liable to cause excess lapping or overlapping.
In order to cope with the demand for higher recording density, a glass substrate, a ceramic substrate, or the like, are frequently used in place of an Ni-P substrate. However, these substrates are generally brittle and have a high hardness, therefore, when texture is imparted by the above-described mechanical system, the substrate may be disadvantageously damaged or broken. Furthermore, this system cannot ensure precise control of the asperity form, therefore, it is very difficult to satisfy both the CSS properties and the low flying height requirement of the magnetic head at the same time.
For example, U.S. Pat. No. 5,108,781 describes a technique of preparing and polishing a Ni-plated aluminum substrate and imparting texture to the polished substrate surface by laser heating. According to this method, the protective film of the magnetic disk obtained replicates the texture of substrate, therefore, stiction occurring when the head (slider) is stopped on the protective film can be reduced. However, in this method, polishing and laser texturing of the substrate are essential matters, therefore, not only the production process of disk is complicated but also the production cost increases.
On the other hand, U.S. Pat. No. 5,053,250 describes a method of forming an underlayer having asperities in situ on a disk substrate. According to this method, a low melting point metal (for example, gallium) is adhered to a heated substrate by sputtering and an underlayer comprising disconnected liquid balls of a low melting point metal (a structure having a stripe pattern of asperities) is formed thereon. After the liquid balls are solidified, a magnetic recording film and a protective film are formed in this order on the underlayer having asperities, then, the asperities on the underlayer surface are replicated and a textured surface is accomplished on the head/disk interface of disk. However, in this method, unless the conditions in texturing such as formation of underlayer are controlled with great care, the crystal growth of the magnetic recording film obtained may be adversely affected. In addition, in this method, the size and cycle of surface asperities are small or the recess depth has an excessively uniform distribution, therefore, the coefficient of friction is not reduced as expected and the CSS properties are not necessarily satisfied.
The object of the present invention is to solve the above-described various problems in conventional texturing techniques.
Accordingly, one object of the present invention is to provide a medium substrate, with a texture, which can be suitably used in the production of a magnetic recording medium or the like capable of high-density recording, can be produced easily, stably and at a low cost, and can satisfy both the CSS properties and the low-floating requirements of a magnetic head.
Another object of the present invention is to provide a method for producing the medium substrate.
Further, another object of the present invention is to provide a magnetic recording medium using the medium substrate.
Furthermore, another object of the present invention is to provide a method for producing the magnetic recording medium using the medium substrate.
In addition, still another object of the present invention is to provide a magnetic disk device using the magnetic recording medium.
The above-described objects and other objects of the present invention will be easily understood from the following detailed description.
As a result of extensive investigation to attain the above-described objects, the present inventor has found that it is effective to select a borosilicate glass mainly comprising silica as the substrate material, heat-treat the glass to cause phase separation and subsequently treat it with an acid to form a texture of pores and also found that the density and size of the formed texture of pores can be easily controlled by controlling the heat-treatment temperature and heat-treatment time.
In one aspect thereof, the present invention resides in a medium substrate for use as a substrate in magnetic recording mediums and the like, comprising a borosilicate glass containing silica as a main component and having on the surface thereof a continuous texture derived from the porous structure.
In another aspect thereof, the present invention resides in a method for producing a medium substrate comprising a borosilicate glass containing silica as a main component and having on the surface thereof a continuous texture derived from the porous structure, the method comprising heat-treating a disk-like borosilicate glass to cause phase separation and treating the glass after the phase separation with an acid to dissolve out the phase separation components and thereby render the borosilicate glass porous.
Further, in another aspect thereof, the present invention resides in a magnetic recording medium comprising a substrate having applied thereon at least a magnetic recording layer, said substrate comprising a borosilicate glass containing silica as a main component and having on the surface thereof a continuous texture derived from the porous structure.
Furthermore, in another aspect thereof, the present invention resides in method for producing a magnetic recording medium comprising a substrate having applied thereon at least a magnetic recording layer, =p the method comprising heat-treating a borosilicate glass disk to cause phase separation and treating the phase separated glass with an acid to dissolve out the phase separation components, thereby producing a substrate comprising a borosilicate glass containing silica as a main component and having on the surface thereof a continuous texture derived from the porous structure produced upon said acid treatment.
In addition, in still another aspect thereof, the present invention resides in a magnetic disk device comprising a recording head part for recording information in a magnetic recording medium and a reproducing head part for reproducing the information, wherein the magnetic recording medium is a magnetic recording medium comprising a nonmagnetic substrate having provided thereon a magnetic recording layer and the substrate comprises a borosilicate glass containing silica as a main component and having on the surface thereof a continuous texture derived from the porous structure.